The present invention relates to ultra-high frequency (UHF) hybrid mixers making it possible to obtain from two radio signals a third radio signal, whose frequency is equal to the difference of those of the first two signals. Such mixers are particularly useful for coherent Doppler radars in which all the signals are obtained from a local crystal oscillator, whose frequency and phase are very stable.
In a special construction of such a radar, a double frequency change is used in the reception chain. The first frequency change is carried out by means of a mixer, which receives on the one hand the reception signal, whose frequency is between 9300 and 9900 MHz and on the other hand a signal from the transmission chain, whose frequency is between 7440 and 8040 MHz. The choice within these ranges takes place on transmission and the frequency difference between these two signals is constant and equal to 1860 MHz.
This is the frequency of the signal resulting from this mixture and obtained at the mixer output. It is relatively high and consequently special precautions must be taken in connection with the construction of the mixer in order to prevent losses and mismatches liable to too greatly attenuate the thus obtained intermediate frequency signal.